Abstract

We simultaneously measure the intensity modulation level and the optical spectrum of the output of a multiple quantum well modulator, and use these data to deduce the electro‐optic coefficients. The effect is quadratic, with a measured ‖s33‖=4.6×10−13 cm2/V2 at a wavelength 12 meV below the band gap. This is approximately 800 times the coefficient measured further from the band gap. We are able to achieve a fractional change in the refractive index of 3.7%. Despite the size of this effect, when we operate the device as an intensity modulator, we observe a linewidth enhancement factor of α=1.0, which means the chirp induced in the device’s output will be small.